The invention relates to fluorous phosphines and a process for their preparation. The invention also relates to the metal complexes based on the fluorous phosphines, methods for the preparation of metal complexes, to catalysts based on the fluorous phosphines and the use of said catalysts in catalysis.
In catalysis, homogeneous catalytic systems are often preferred over heterogeneous ones because of their better product and substrate selectivity. A general problem in homogeneous catalysis, however, is separation and recycling of the catalyst. This has led to the development of several supported catalytic systems, e.g. immobilised versions of homogeneous catalysts on inorganic supports (M. G. L. Petrucci, A. K. Kakkar, Adv. Mater., 1996, 8, 251 and references cited therein, W. A. Herrmann, B. Cornils, Angew. Chem. Int. Ed. Engl, 1997, 36, 1098 and references cited therein) and systems connected to polymers or dendrimers (J. W. Knapen, A. W. Van der Made, J. C. Wilde, P. W. N. M. van Leeuwen, P. Wijkens, D. M. Grove, G. van Koten, Nature, 1994, 372, 659), with the combined advantages of both homogeneous and heterogeneous catalysis. Another elegant solution for this separation/recycling problem is the aqueous biphasic Ruhrchemie/Rhxc3x4ne-Poulenc process (W. A. Hermann, C. W. Kohlpaintner, Angew. Chem. Int. Ed. Engl., 1993, 32, 1524). In this process a water soluble version of the conventional Rh/PPh3 catalyst is used, i.e. TPPTS/Rh (TPPTS=P(m-C5H4SO3Na)3). The catalytic process is performed under biphasic conditions with the aqueous phase containing the catalyst, and the organic phase containing the products. The catalyst can be easily removed from the products by phase separation. In this process losses of rhodium are kept below 10xe2x88x926 mg/kg of product produced.
Despite the advantage of aqueous biphasic systems in catalysis, they also have some disadvantages. Some reactants or catalysts hydrolyze when exposed to water, resulting in decreased performance for these systems. Furthermore, due to the two phase nature of the system, the catalyst is not homogeneously mixed with the products. Therefore, the reactants or catalysts have to cross or react at the phase boundary which could lead to mass flow limitations, resulting in considerable lower reaction rates as compared to single phase homogeneous systems. This effect is enhanced by the often low solubility in water of organic substrates with higher molecular weights (I. T. Horvxc3xa1th, J. Rxc3xa1bai, Science, 1994, 266, 72).
The special physical properties of perfluorinated compounds and the problem associated with aqueous bi-phasic catalysis inspired Horvxc3xa1th et al. to use fluorous bi-phase systems in rhodium catalysed hydroformylation (I. T. Horvxc3xa1th, J. Rxc3xa1bai, Science, 1994, 266, 72). Here, the fluorous phase, as an alternative to aqueous phase, denotes a solvent, which is rich in Cxe2x80x94F bonds. Below a certain temperature the fluorous phase does not mix with an organic phase containing the reactants and products. At a certain temperature, the system consists of a fluorous phase, containing a fluorous phase soluble catalyst, and a hydrocarbon phase, containing the reactants. Above this temperature, the two phases mix to form one phase allowing efficient homogeneous catalysis to proceed. Catalyst recovery and product separation can then be achieved by cooling of the reaction mixture below the temperature where phase separation occurs. Alternatively, if e.g. the phase transition temperature of a certain fluorous bi-phasic system is too high, or if desirable for other reasons, the catalytic reaction can also be performed under bi-phasic conditions.
For reactions which cannot be performed in an aqueous bi-phasic system, e.g. due to low solubility of reactants in the aqueous layer, diffusion limitations or water sensitive components a fluorous bi-phasic system could be an alternative. Perfluoro solvents do not usually mix with water and can contain water only on the ppm level (see D. W. Zhu, Synthesis, 1993, 953).
To render a catalyst preferentially soluble in a fluorous phase, it is usually functionalised with one or several perfluoroalkylgroups, also sometimes referred to as ponytails or pigtails. Most often, perfluorohexyl (C6F13) and perfluoro-octyl (C8H17) groups are being used. The length and the number of perfluoroalkylgroups are important because they influence the solubility of perfluoralkylated compounds in a fluorous solvent.
Usually the reactivity and selectivity of homogenous catalysts are modified by reacting the catalytically active metal with different coordinating ligands. A widely used class of ligands for these purposes are phosphines. A serious drawback of the use of perfluorinated ponytails in ligands in general are the strong electron withdrawing properties of perfluoroalkyl functions. These properties can influence the coordinating characteristics of the phosphor atom and hence the resulting catalytic activity dramatically.
In order to reduce undesired effects of the perfluorinated ponytails on the activity of the catalyst, spacers have been introduced. The spacers which have been developed so far comprise ethylene, propylene or substituted phenyl, such as for instance described in I. T. Horvxc3xa1th, J. Rxc3xa1bai, Science, 1994, 266, 72; European Patent application 94-304877.7, U.S. Pat. No. 9,388,706; Bhattacharya, D. Gudmundsen, E. G Hope, R. D. W Kemmit, D. R. Paige. A. M. Stuart, J. Chem. Soc. Perkin Trans. I, 1997, 3609; J. J. J Juliette, I. T. Horvxc3xa1th, J. A. Gladysz, Angew. Chem. Int. Ed. Engl, 1997, 36, 161; S. Kainz, D. Koch, W. Baumann, W. Leitner, Angew. Chem. Int. Ed. Engl, 1997, 36, 1628.
However, there continues to be a need for more variations of these spacers for a more delicate tuning of ligands also because the existing catalyst systems with fluorous ligands often have lower activity when compared with their non-fluorous counterparts or analogues.
It is therefore a goal of the present invention to provide for fluorous ligands with different spacer groups. It is a further goal of the invention to provide for ligands with spacers which can reduce or even nullify the effect of the perfluorinated ponytails of the ligand on the catalytic activity. It is another goal of the present invention to overcome the above-mentioned disadvantages of other approaches and to provide for ligands who will allow efficient product-catalyst separation when applied in catalysis
It has now been found that the use of certain non-carbon fragments in the spacer results in ligands that further enhance the applicability of the ponytail tailored ligands and of catalysts based thereon for use in homogeneous catalysis.
Accordingly, the invention relates to a fluorous phosphine wherein at least one phosphor atom is coupled to at least one aryl or alkyl moiety, to which moiety a fluorous tail is coupled, wherein a spacer group, containing a non-carbon atom, is positioned between the aryl or alkyl moiety and the fluorous tail.